Add google analytics sample data

[AdRiley]

Pull Request Description

This adds a new Google_Credential type of Sample. Which when passed to supporting components (like Google analytics) makes that component produce sample data. This can then be used to publish example workflows.

Sample data is fairly basic right now, but could be extended in the future.

Important Notes

Checklist

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[radeusgd]

I'm wondering if it wouldn't be better to have a separate type (e.g. Google_Sample_Data_Source) and if a method supports the 'sample' mode, it could take credentials : Google_Credential | Google_Sample_Data_Source clearly indicating that either is accepted.

This way, we can easily indicate in the type if the sample mode is available or not.

In the current state, it will only be seen at runtime.

[AdRiley]

Yeah. It's a fair suggestion. Can't decide if it is better or not. I think generally this will only be used in workflows that we have built as samples so it's probably unlikely that a user will actually build a workflow using it.

Think I'm going to merge this one as is for now.

[radeusgd]

so it's probably unlikely that a user will actually build a workflow using it.

I guess that suggests that keeping it separate may be a good idea.

[radeusgd]

Looks OK.

One idea about the API - I'm concerned if having the Sample available in all kinds of operations we'll have in the future will be that good. But I'm not really sure if it's a problem, so please treat as a light optional suggestion - I'm not 100% convinced my suggestion is really better than the current approach.